Integrated circuits may comprise memory. Integrated memory is usually fabricated in one or more arrays of individual memory cells. The memory cells have at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
One type of memory cell utilizes a transistor (or other suitable select device) in combination with a resistor. The resistor is a memory storage element and comprises programmable material. The memory may be incorporated into Resistive Random Access Memory (RRAM).
Numerous programmable materials are known which can be suitable for utilization in resistive memory storage elements. For instance, phase change materials (such as, for example, various chalcogenides) may be utilized as programmable materials in phase change memory (PCM). As another example, some programmable materials may utilize ions as mobile charge carriers to transition from one memory state to another.
There may be advantages for utilizing bipolar junction transistors (BJTs) as select devices. Such advantages may include improved ability to pass programming current relative to other types of select devices; improved current density relative to other types of select devices; improved scalability relative to other types of select devices and/or improved access speed through BJTs relative to other types of select devices.
It would be desirable to develop improved methods for incorporating BJTs as select devices. It would also be desirable to develop improved memory array architectures incorporating BJTs as select devices.